What is CNC Machining & Their Working, Operation, Parts, Types

Hello, friends in this article you will know what is CNC machining and how CNC Machining works along with this we will also know their operation, parts, types, applications, advantages, disadvantages, and many more.

Many objects like airplanes, robots, space rockets, cars, and boats are made with the help of a manufacturing technique called CNC machining.

CNC machining is preferred by engineers worldwide because it is one of the most precise manufacturing techniques.

If you're an engineer, you are probably quite familiar with CNC machining.

CNC machining is a subtractive manufacturing technique because parts are manufactured by removing material from a solid block or called a blank or workpiece. 

Almost any type of hard material can be machined through CNC. Some of the most common materials are aluminum, brass, ABS, Delrin, and nylon.

What is CNC Machining?

CNC Machining, also known as Computer Numerical Control Machining, is a digital manufacturing technology that provides high-accuracy parts directly from CAD files.

It can rotate all machining tools around various numbers of axes, such as 3 axes or 5 axes.

The basic CNC process can be broken down into the following steps:

  1. First, an engineer designs the CAD model of the part.
  2. Then the machinist turns the CAD file into a CNC program which is called the G-code and with this G-code, the machinist sets up the CNC machine.

During manufacturing, CNC machining tools such as mills, lathes, grinders, and routers are automated and controlled by a computer. 

This means little human supervision is needed during the manufacturing process. 

What is CNC Machining

In CNC machining, programs are designed or prepared first, and then it is fed to the CNC machine. According to the program, the CNC controls the motion and speed of the machine tools.

Main parts of CNC Machining

There are the following main parts of CNC machining:

  • Input Devices
  • Machine Control Unit (MCU)
  • Machine Tool
  • Driving System
  • Feedback System

Show in the figure the parts of CNC machining are described below in detail.

main parts of CNC machining

 Input Devices

These are the devices that are used to input the part program in the CNC machine. 

There are three commonly used input devices and these are punch tape reader, magnetic tape reader, and computer via RS-232-C communication.

Machine Control Unit (MCU)

It is the heart of the CNC machine. It performs all the controlling actions of the CNC machine.

Machine Tool

A CNC machine tool always has a sliding table and a spindle to control the position and speed. 

The machine table is controlled in the X and Y-axis directions and the spindle is controlled in the Z-axis direction.

Driving System

The driving system of a CNC machine consists of amplifier circuits, drive motors and ball lead screws.

Feedback System

This system consists of transducers that act like sensors. It is also called a measuring system. 

It contains position and speed transducers that continuously monitor the position and speed of the Cutting tool located at any instant.

How CNC Machining Works

How CNC Machining Works

  1. First, the part programming is fed into the CNC's MCU.
  2. The MCU processes all the data and according to the program prepared, it generates all the motion commands and sends them to the driving system.
  3. The motion system works as a motion command sent by the MCU. The drive system controls the speed and velocity of the machine tool.
  4. The feedback system records the position and velocity measurement of the machine tool and sends a feedback signal to the MCU.  
  5. In the MCU, the feedback signals are compared with the reference signals and if there are errors, it corrects them and sends new signals to the machine tool to be corrected.
  6. A display unit is used to view all commands, programs, and other important data. It acts as the eye of the machine.

Classification of CNC Machining System

There are the following types of CNC machining:

  • Based on Feedback or Type of Control System
  • Based on Control System Characteristics
  • Based on Positioning Co-Ordinates System
  • Based on the number of axes 2, 3, 4 & 5 axes CNC machines.
  • Based on the power supply Electric, Hydraulic & Pneumatic systems

Based on Feedback or Type of Control System

  • Open Loop System
  • Closed Loop System

Show in the figure the open-loop and closed-loop systems are described below in detail.

classification of CNC machining system

Open Loop System

The open-loop control systems do not have a feedback mechanism. The open-loop machine tool controls have only motion control but do not have any provision for feedback, which needs to be compared with the input for better control and correction of the drive system.

Closed Loop System

The closed-loop control systems have a feedback mechanism. The closed-loop machine tool controls have motion control with a provision of feedback, which can be used for accurately controlling the drive system by comparing it with the input information until the required or desired position is achieved.

Based on Control System Characteristics

  • Point-to-Point Position System
  • Straight Line System
  • Contouring

Show in the figure: 

CNC machining system types

Point-to-Point Position System

In this method, the cutting tool moves from one point to another point.

Machining is done only at desired points. No machining is done when the spindle moves from one point to another point.

Straight Line System

Straight-line systems are capable of moving the cutting tool parallel to one of the axes(X-Y-Z) at a controlled feed rate suitable for machining.

Straight-line systems can also perform a point-to-point movement.

Contouring

In this system, the motion of the tool and the workpiece are controlled along many axes, simultaneously(X-Y-Z)

This facilitates the machining of different types of curved surfaces, profiles, and taper or angular cuts.

Based on Positioning Co-Ordinates System

  • Absolute System
  • Incremental system

Shown in the figure are absolute and incremental systems.

CNC machining types

Absolute System

In this system, all the moving commands are referred to one reference point, which is the origin and is called the zero point.

This system is also known as a fixed zero system.

Incremental system

In an incremental system, the coordinates of any points are calculated with reference to the previous position of the tool.

It is also known as a floating zero system.

Based on the number of axes 2, 3, 4 & 5 axes CNC machines.

  • 2 & 3 axes CNC machines
  • 4 & 5 axes CNC machines

2 & 3 axes CNC machines

CNC lathes will be coming under 2 axes machines. There will be two axes along which motion takes place. The saddle will be moving longitudinally on the bed (Z-axis) and the cross slide moves transversely on the saddle (along X-axis). 

In 3-axes machines, there will be one more axis, perpendicular to the above two axes. With the simultaneous control of all the 3 axes, complex surfaces can be machined.

4 & 5 axes CNC Machines

4 and 5 axes CNC machines provide multi-axis machining capabilities beyond the standard 3-axis CNC tool path movements. A 5-axis milling center includes the three X, Y, and Z axes, the A axis which is a rotary tilting of the spindle, and the B-axis, which can be a rotary index table.

Based on the power supply Electric, Hydraulic & Pneumatic systems

A mechanical power unit refers to a device that transforms some form of energy to mechanical power, used for driving slides, and saddles forming a part of the machine tool. 

The input power may be electrical, hydraulic, or pneumatic.

Types of CNC Machining Operations

  • Lathe
  • Milling
  • Grinding
  • Turning
  • Drilling
  • Routing
  • Lapping
  • Honing
  • Unconventional Machining

Show in the figure some CNC machining operations.

Types of CNC Machining Operations

Lathe

A lathe is mainly used for machining circular surfaces such as cylindrical or conical but it can also be used for making flat surfaces, drilling holes, machining slots, and many other types of work.

Milling

Milling is a method in which the material is cut by feeding the workpiece under a rotating multiple-tooth cutter and producing a machined surface that may be flat, angular, or curved.

Grinding

Grinding is a finishing operation which is to give the required accuracy and precision by removing the extra material.

Turning

In the turning operation, the workpiece is turned when it is made to rotate about the lathe axis.

Drilling

In this drilling operation, the workpiece is held stationary which means clamped in position and drill bits rotate to make a hole. 

Routing

A CNC router is similar to a CNC milling machine in that it also has a rotating piece cutting head, but a router is used to cut soft materials that don't require a lot of precision.

Lapping

Lapping is a machining process that is used to improve surface finish by reducing roughness, waviness, and other types of irregularities on the surface. 

Honing

Honing is an abrasive machining process used to finish the cylindrical surface of a metal workpiece by rubbing an abrasive grinding stone or grinding wheel with a controlled path.

Unconventional Machining

An unconventional machining process is a very special type of machining process because in this process there is no direct contact between the tool and the workpiece.

Application

Almost every manufacturing industry uses CNC machines. 

With an increase in the competitive environment and demands, the demand for CNC usage has increased to a greater extent. The machine tools that come with the CNC are lathes, mills, shapers, welding, etc. 

The industries that are using CNC machines are the automotive industry, metal-removing industries, industries of fabricating metals, electrical discharge machining industries, wood industries, etc.

Advantages of CNC Machining

  1. It can produce jobs with the highest accuracy and precision than any other manual machine.
  2. It can be run 24 hours a day.
  3. A highly skilled operator is not required to operate a CNC machine.
  4. Operators can easily make changes and improvements and reduce the delay time.
  5. It has the capability to produce complex designs with high accuracy in the minimum possible time.
  6. Modern design software such as CAD, and CAM allows the designer to simulate the manufacturer of his/her idea.
  7. Fewer workers are required to operate a CNC machine and save labor costs.

Disadvantages of CNC Machining

  1. The cost of CNC machining is very high compared with a manually operated machine.
  2. The parts of the CNC machines are expensive.
  3. The maintenance cost in the case of CNC machining is quite high.
  4. It does not eliminate the need for costly tools.


So here you have to know all aspects related to CNC machining. 

If you have any doubts then you are free to ask me by mail or on the contact us page.


Thank You.

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